Generally speaking, an alpine ski has several deformation capabilities. For instance, it is possible to determine a longitudinal flexural rigidity, which corresponds to the capability of the ski to bend when it is subjected to a vertical force. This bending is utilized in particular when the ski has to follow the changes in gradient of the run and also during turning.
A ski also has a torsional rigidity, which corresponds to its deformation capability when it is subjected to a torque applied about an axis essentially parallel to the ski. This deflection capability allows slight twisting of the ends of the ski.
Furthermore, a ski has a lateral flexural rigidity, which corresponds to its deformation capability when it is subjected to a lateral force. This lateral flexural rigidity is particularly small on existing skis in view of the fact that the width of a ski is markedly greater than its thickness.
There has thus far been a distinct trend toward producing skis which have a particularly deep sidecut and a small length. This sidecut forms on each side of the ski a curve which is comparable to an arc of a circle of which the radius of curvature is frequently smaller than about 24 meters. Generally speaking, the radius of curvature of this sidecut is defined by the radius of the circle passing through three points which are the two points of maximum width at the tip and at the tail and the point of minimum width at the underfoot.
This deep sidecut makes it possible when performing “cut turns” or “carving” to put the ski into a turn having a given radius, which depends therefore on the radius of curvature of this sidecut, minimizing the effects of sideslipping.
Performing carving requires the skier to lean laterally to a very considerable extent and to exert great forces during turning in order to cut into the snow to the maximum possible extent with the edge line. Such turns therefore result in high speed and are consequently beyond the scope of the average skier.
If the speed and the force exerted on the edge by the skier are insufficient, the edges cut into the snow only at the two points of maximum width of the sidecut and possibly over a small part of the sidecut. Outside these zones, the sidecut is in a state of sideslipping. The handling of the turn is therefore not truly optimum.
One object of the invention is to make it possible for the edge to bite over a major part of the sidecut, whatever the radius of curvature of the turn, the inclination of the ski in relation to the snow and the speed of the skier.
In the past, it has already been proposed to produce skis with special constructions which favor longitudinal deflection of certain parts of the ski, in particular the ends. For instance, in document AT 23 80 74, a ski has been described which has a front part which is split, so that each of these parts can move vertically independently of the other. This arrangement makes it possible to reduce the longitudinal flexural rigidity of each of the ends of the ski. However, the side profile of such a ski remains constant, in this case being rectilinear. Thus, as touched on above, when the ski is put into the turn, only a very limited zone of the edge bites into the snow, the remainder of the side profile sideslipping, or not being in contact with the snow.
A similar approach has also been proposed in document DE 34 44 345. The ski described in this document comprises a slit extending longitudinally from the tip to the tail in order to allow a reduction in the overall torsional rigidity. This ski also has reduced longitudinal flexural rigidity since, when the ski is inclined laterally in relation to the snow, only half of the ski comes into contact with the snow and therefore has a useful rigidity.
The design of the ski described in document FR 2 227 883 also aimed to achieve a similar goal.
A ski having a longitudinal slit opening at the end of the tip or of the tail has also been described in document FR 2794374. Means are provided for modifying the gap between the two portions separated by the slit and therefore for modifying the sidecut of the ski before use according to the capabilities of the skier and to the type of skiing performed.
A ski having a mechanical device located inside a housing formed inside the ski has also been described in document EP 1 297 869. This device is intended to increase the separation between the left and right edges when the ski bends.